Heat pump arrangement and method for operating heat pump arrangement

ABSTRACT

A heat pump arrangement including a first heat pump through which a first fluid flows, a second heat pump through which a second fluid flows, and a heat exchanger to transfer heat from the first fluid to the second fluid. The heat is transferred from the first fluid to the second fluid at a fluid temperature of at least 120° C. for the second fluid. The first fluid and the second fluid each have a volumetric heating capacity of at least 500 kJ/m3 when the heat is transferred from the first fluid to the second fluid. Useful heat is extracted from the second fluid at a fluid temperature of at least 120° C. for the second fluid, and the first fluid and the second fluid each have a volumetric heating capacity of at least 500 kJ/m 3  when the useful heat is extracted.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to International Application No. PCT/EP2014/061528 filed on Jun. 4, 2014 and German Application No. 10 2013 211 087.1 filed on Jun. 14, 2013; the contents of both are hereby incorporated by reference.

BACKGROUND

Heat pump arrangements are used for industrial heat provision. A heat pump is a machine which, by using technical work, absorbs thermal energy in the form of heat at a lower temperature from a heat source and, together with the drive energy of a compression machine, releases it as waste heat at a higher temperature to a heat sink. For temporary storage or to transfer heat, a fluid is used, which is conveyed within the heat pump in a cycle process by the compression machine. This cycle process is also known as a thermodynamic vapor compression cycle.

In the absence of suitable fluids and suitable compression machines for high temperature heat pumps (HTHP), the useful heat from heat pumps which are currently commercially obtainable is limited to temperatures of up to at most 100° C.

SUMMARY

Various embodiments described herein relate to a method and a heat pump arrangement by which useful heat at particularly high temperatures may be provided.

Various embodiments described herein relate to a method for operating a heat pump arrangement in which a first fluid flows through a first heat pump, a second fluid flows through a second heat pump, and heat is transferred from the first fluid to the second fluid using a heat exchanger.

Useful heat is extracted from the second fluid at a fluid temperature of at least 120° C., wherein the useful heat of the second fluid is released at a volumetric heating capacity of the first fluid and of the second fluid of at least 500 kJ/m³. The volumetric heating capacity (VHC) is crucial for the theoretically achievable coefficient of performance (COP) of heat pumps. The higher the VHC, the more efficiently the heat pump thus operates. Thus, the higher the volumetric heating capacity is above the stated 500 kJ/m³, the higher also is the coefficient of performance (COP) of the respective heat pump. By the second heat pump, particularly high fluid temperatures may be achieved. As a consequence, useful heat at a particularly high temperature may be extracted from the second fluid as a function of the heat transferred by the first fluid.

Various embodiments described herein provide for the useful heat to be extracted from the second fluid at a fluid temperature of at least 150° C., and particularly of at least 160° C. By using a second heat pump, particularly high fluid temperatures may be achieved. Consequently, useful heat at a particularly high temperature may be extracted from the second fluid, whereby useful heat may be provided all the more effectively for industrial use.

According to various embodiments described herein, at least one fluoroketone flows through the first heat pump as the first fluid. Fluoroketones are particularly safe to use in industry, since there is no need to take special protective measures in the event of an incident. Since the use of fluoroketones is not governed by environmental requirements, use thereof is particularly future-proof. Moreover, they have a particularly low global warming potential and are non-flammable and non-toxic. For this reason, fluoroketones are particularly suitable for use as fluids in heat pump arrangements, in particular if industrial process heat, in particular useful heat at a temperature of greater than 120° C., is provided using these heat pump arrangements.

According to various embodiments described herein, water or at least one fluoroketone is used as the second fluid. Since they are both environmentally friendly and unobjectionable from the point of view of safety, both water and fluoroketones are suitable in particular as fluids in applications in which high fluid temperatures occur, given that they are neither flammable nor toxic.

According to various embodiments described herein, different fluids are used as the first and second fluids. The coefficient of performance (COP) of the respective heat pump depends on the respective temperature rise. The temperature rise of a heat pump is understood to mean the temperature difference which may be achieved between a respective condenser of the heat pump and a respective evaporator of the heat pump. In accordance with the achievable temperature rise of the first heat pump, waste heat at a particularly high temperature may thus be provided and transferred by the heat exchanger to the second fluid of the second heat pump. The maximum temperature of the second fluid which can be reached using the second heat pump thus depends directly on the quantity of heat transferred by the first fluid. Particularly high coefficients of performance may be achieved using particularly large temperature rises of the respective heat pump, wherein it is advantageous for fluids of different composition to be used in each case for the first and second fluids. If fluid temperatures of at most 140° C. are to be achieved using the first heat pump, the use of fluoroketone NOVEC 524 is particularly recommended. Fluoroketone NOVEC 524 has a particularly high volumetric heating capacity (VHC) in the range from 100° C. to 140° C. Since, however, NOVEC 524 is suitable only up to the stated maximum fluid temperature of 140° C., in order to achieve a temperature rise from 140° C. to 200° C. using the second heat pump, it is recommended that water be used as the second fluid, water also being suitable for greater fluid temperatures than 140° C.

According to various embodiments described herein, the heat release from the first to the second fluid proceeds largely isothermally. Through isothermal heat release, the temperature of the released quantity of heat is kept particularly constant, whereby temperature fluctuations are particularly largely ruled out and thus also a largely constant temperature rise may be achieved using the second heat pump. To achieve isothermal heat release using the heat exchanger, the first fluid has to be operated sub-critically, i.e. the first fluid can only be used below its critical temperature. Thus, the first fluid has to be operated at a temperature at which both the liquid and the gaseous physical states may be present.

According to various embodiments described herein, the useful heat is released at a volumetric heating capacity of at least 1000 kJ/m³, possibly of at least 1200 kJ/m³ and possibly of at least 1500 kJ/m³ of the second fluid. Although the theoretically achievable coefficient of performance (COP) depends on the design of a compression apparatus of which the respective fluid of the respective heat pump is compressed, the fluid in the heat pump arrangement should be operated at a point at which a volumetric heating capacity of at least 1000 kJ/m³ is present. The higher the volumetric heating capacity above the stated 1000 kJ/m³, the higher too is the coefficient of performance (COP) of the respective heat pump. If at least 1000 kJ/m³ are needed for the volumetric heating capacity of the respective fluid, water at a temperature of below 150° C. cannot sensibly be used as the fluid. If a volumetric heating capacity of at least 1500 kJ/m³ is present for a respective fluid, the coefficient of performance (COP) of the respective heat pump is particularly great.

In the heat pump arrangement with at least one first heat pump through which a first fluid flows, and a second heat pump through which a second fluid flows, heat may be transferred from the first fluid to the second fluid using a heat exchanger.

Useful heat may be transferred using the second fluid at a fluid temperature of at least 120° C., wherein the first fluid and the second fluid have a volumetric heating capacity of at least 500 kJ/m³. The higher the volumetric heating capacity, the greater too is the achievable coefficient of performance (COP) of the respective heat pump. Useful heat at a particularly high temperature may in this case be extracted from the second fluid as a function of the heat transferred by the first fluid. To provide a heat pump arrangement, which is also known as a heat pump cascade, in which the second heat pump may provide useful heat at a particularly high temperature, a maximally high volumetric heating capacity of the first fluid of the first heat pump is favorable, wherein it is favorable if the quantity of heat transferred from the first to the second fluid is transferred at a particularly high temperature.

In various embodiments of the heat pump arrangement described herein, at least one temperature rise resulting from a relatively high pressure ratio of the first fluid and/or the second fluid may be increased by at least two-stage compression. If particularly large temperature rises are to be achieved with a fluid in a heat pump, two- or multistage compression is recommended. In this case, intermediate cooling may be fitted between the compression apparatuses effecting the respective compression stage. This is sensible in particular where water is used as the fluid. The heat of the intermediate cooling may be fed in a particularly energy-efficient manner to an evaporation apparatus of the respective heat pump. To bring about very high temperature rises, cascades of more than two heat pump circuits are also possible.

According to various embodiments of the heat pump arrangement described herein, the second fluid is largely isothermally compressible using a liquid ring compressor. Compression of the fluid may proceed largely isothermally using a liquid ring compressor. The liquid ring of the liquid ring compressor is then in direct contact with the fluid to be compressed, whereby heat of compression may be transferred particularly effectively from the fluid to the ring liquid from which the liquid ring is formed. The heat transfer resistance is thus particularly low, since the fluid and the ring liquid are not divided from one another by a wall.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages will become more apparent and more readily appreciated from the following description of the various embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic representation of a heat pump cascade according to the related art, which corresponds to a heat pump arrangement with in the present case two heat pump circuits;

FIG. 2 is a schematic diagram of the respective curves of the volumetric heating capacities of various fluids of the heat pump arrangement plotted against temperature; and

FIG. 3 is a schematic representation of a heat pump cascade which corresponds to a heat pump arrangement with two heat pump circuits, wherein one of the heat pump circuits is operated with a fluoroketone as fluid.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the various embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

FIG. 1 is a schematic representation of a heat pump arrangement which comprises two heat pump circuits and is known in accordance with the related art as a cascade heat pump 1. The cascade heat pump 1 includes a first heat pump 2 through which a first fluid flows and a second heat pump 3 through which a second fluid flows. The first and second fluids are coupled together for heat transfer by a heat exchanger 19. The heat exchanger 19 includes a condenser 6 of the first heat pump 2 and an evaporator 8 of the second heat pump 3. The first fluid of the first heat pump 2 is evaporated by an evaporator 4, wherein the evaporator 4 is supplied with thermal energy by a heat source 12. The first fluid heated by the evaporator 4 is delivered in the direction of an arrow 14 by the first heat pump 2 by a compressor 5 of the first heat pump 2. Then, the heated and compressed first fluid in the condenser 6 releases heat to the evaporator 8, wherein the second fluid of the second heat pump 3 is evaporated by the evaporator 8. Subsequent to this release of heat, the first fluid is expanded by an expansion valve 7 of the first heat pump 2 and thereupon once again absorbs heat through the evaporator 4. The circuit of the first heat pump 2 is thus closed. The second fluid of the second heat pump 3 heated by the heat exchanger 19, i.e. by release of heat by the condenser 6 of the first heat pump 2 to the evaporator 8 of the second heat pump 3, is compressed by a compressor 9 of the second heat pump 3 and in a condenser 10 of the second heat pump 3 releases heat to a heat sink 13. Then, the second fluid flows in the direction of an arrow 15 through an expansion valve 11 of the second heat pump 3 and is expanded there. Then, the second fluid again absorbs heat by the heat exchanger 19 and the circuit of the second heat pump 3 is thus closed.

FIG. 2 is a schematic diagram of different curves of volumetric heating capacities, wherein the y axis of the diagram plots a volumetric heating capacity 20 and the x axis plots a fluid temperature 21, which corresponds to the condensing temperature of the fluid. FIG. 2 shows that a heating capacity curve 16, which corresponds to the heating capacity curve of a fluoroketone known as NOVEC 524, in each case has higher values for the same fluid temperatures 21 than a heating capacity curve 17, which corresponds to the heating capacity curve of a fluoroketone known as NOVEC 649. As is clear from the diagram, neither the heating capacity curve 16 nor the heating capacity curve 17 extends over the entire length of the x axis, on which the fluid temperature 21 is plotted. Thus, the heating capacity curve 16 of the fluoroketone NOVEC 524 is limited by reaching a critical point 28 at 148° C. and the heating capacity curve 17 of the fluoroketone NOVEC 649 is limited by reaching a critical point 29 at for instance 169° C. Although, as is clear from the diagram, a heating capacity curve 18 which corresponds to the heating capacity curve of water has the lowest volumetric heating capacity 20 in each case for the same fluid temperatures 21 compared with the two fluoroketones, water may be used over a particularly wide range of fluid temperatures 21, without the critical point thereof being reached. As is additionally clear from FIG. 2, although the heating capacity curve 18 of water at fluid temperatures below the critical point 28 and the critical point 29 is respectively below the heating capacity curve 16 and the heating capacity curve 17, the heating capacity curve 18 of water rises at high fluid temperatures 21 to greater values than can be achieved with the heating capacity curve 16 and the heating capacity curve 17 as a consequence of the respective critical points 28 and 29 respectively being reached. It is moreover clear that a quantity of heat with a working temperature of at least 160° C. may be released by the cascade heat pump 1 to the heat sink 13 if the fluoroketone NOVEC 649 is used as the first fluid of the first heat pump 2. Since, on the basis of the quantity of heat transferred by the heat exchanger 19 from this first fluid to the second fluid at a temperature of up to 160° C., the second fluid of the second heat pump 3 is heated further, a temperature of the useful heat even higher than 160° C. may be reached by the second heat pump 3.

Only subcritically operated fluids are options for the fluid for the first heat pump 2 of the cascade heat pump 1, since heat release from the first fluid to the second fluid should proceed isothermally by the heat exchanger 19. To allow isothermal heat release, the first fluid of the first heat pump 2 is operated at a fluid temperature 21 which lies below the critical temperature of the respective critical point 28 or 29. The higher the volumetric heating capacity 20 of a fluid of one of the heat pumps 2, 3, the more efficiently the respective heat pump 2, 3 operates. Thus, the theoretically achievable coefficient of performance thereof also increases with a respective higher volumetric heating capacity 20.

As is clear when FIG. 2 and FIG. 3 are looked at together, it is particularly advantageous for a fluoroketone 26, such as NOVEC 524, to be used as the first fluid of the first heat pump 2. The fluid temperature 21 to which the fluoroketone 26 is heated remains below the fundamental critical temperature of the critical point 28, in order to allow isothermal heat release by the heat exchanger 19 to the second fluid of the second heat pump 3. Water 27 is used, for example, as the second fluid of the second heat pump 3. The cascade heat pump 1 illustrated in a schematic representation in FIG. 3 substantially includes the components already described in FIG. 1, for which reason only the differences will be examined below.

Instead of the condenser 6 and the evaporator 8, the heat exchanger 19 according to FIG. 3 includes a high temperature condenser 22 of the first heat pump 2 and a high temperature evaporator 23 of the second heat pump 3. Moreover, as is visible in FIG. 3, a liquid ring compressor 24 is used to deliver the water 27, rather than the compressor 9. In the liquid ring compressor 24, the water 27, which has been previously evaporated as the result of an input of heat by the high temperature evaporator, is compressed and supplied to a high temperature condenser 25.

Due to the particularly high volumetric heating capacity of the fluoroketone 26 of over 3000 kJ/m³ and thus markedly over 1500 kJ/m³, a quantity of heat is transferred at a fluid temperature 21 of 140° C. of the fluoroketone 26, which does not exceed the critical temperature of the critical point 28, by the high temperature condenser 22 of the first heat pump 2 to the high temperature evaporator 23 of the second heat pump 3. Thus, a quantity of heat at a particularly high temperature may be released to the water 27 by the high temperature evaporator 23, wherein as a consequence a quantity of useful heat at a particularly high temperature may be released to the heat sink 13 by the high temperature condenser 25. If the water 27 which is conveyed as a fluid in the second heat pump 3 is heated to a temperature of for example 200° C. by the quantity of heat at 140° C. transferred by the heat exchanger 19 from the fluoroketone 26 to the water 27, this corresponds to a rise in temperature of 60° C. of the water 27. At 200° C. the volumetric calorific value 20 of water 27 amounts to over 4000 kJ/m³, i.e. a markedly higher value than 1500 kJ/m³.

The various embodiments have been described in detail with particular reference and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the various embodiments covered by the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide V. DIRECTV, 69 USPQ2d 1865 (Fed. Cir. 2004). 

1-10. (canceled)
 11. A method for operating a heat pump system in which a first fluid flows through a first heat pump, a second fluid flows through a second heat pump, and heat is transferred from the first fluid to the second fluid using a heat exchanger, the method comprising: extracting useful heat from the second fluid at a fluid temperature of at least 120° C. for the second fluid, the first fluid and the second fluid each having a volumetric heating capacity of at least 500 kJ/m³ when the useful heat is extracted.
 12. The method as claimed in claim 11, wherein the useful heat is extracted from the second fluid at a fluid temperature of at least 150° C.
 13. The method as claimed in claim 12, wherein the useful heat is extracted from the second fluid at a fluid temperature of at least 160° C.
 14. The method as claimed in claim 11, wherein the first fluid is a fluoroketone.
 15. The method as claimed in claim 11, wherein the second fluid is one of water and a fluoroketone.
 16. The method as claimed in claim 11, wherein the first fluid and the second fluid are different fluids.
 17. The method as claimed in claim 11, wherein the heat is transferred from the first fluid to the second fluid isothermally.
 18. The method as claimed in claim 11, wherein the first fluid and the second fluid each have a volumetric heating capacity of at least 1000 kJ/m³ when the useful heat is extracted from the second fluid.
 19. The method as claimed in claim 11, wherein the first fluid and the second fluid each have a volumetric heating capacity of at least 1200 kJ/m³ when the useful heat is extracted from the second fluid.
 20. The method as claimed in claim 11, wherein the first fluid and the second fluid each have a volumetric heating capacity of at least 1500 kJ/m³ when the useful heat is extracted from the second fluid.
 21. A heat pump system, comprising: a first heat pump through which a first fluid flows; a second heat pump through which a second fluid flows; and a heat exchanger configured to transfer heat from the first fluid to the second fluid, the heat being transferred from the first fluid to the second fluid at a fluid temperature of at least 120° C. for the second fluid, the first fluid and the second fluid each having a volumetric heating capacity of at least 500 kJ/m³ when the heat is transferred from the first fluid to the second fluid.
 22. The heat pump system as claimed in claim 21, wherein at least one temperature rise of the first fluid and the second fluid is increased by two-stage compression.
 23. A heat pump system as claimed in claim 21, wherein the second fluid is isothermally compressible using a liquid ring compressor. 